1. Field of the Invention
The present invention relates to a magnetoresistance effect device which changes its resistance value according to an external magnetic field, and a magnetic head using the magnetoresistance effect device.
2. Description of the Prior Art
The magnetoresistance device (hereinafter, referred to as MR device) is a device which changes its resistance value according to an external magnetic field, and is used for a magnetic head for reproducing a signal recorded on a magnetic recording medium and a magnetic sensor for detecting intensity and direction of an external magnetic field.
Such an MR device may be an AMR device utilizing the anisotropic magnetoresistance effect or a GMR device utilizing the giant magnetoresistance effect.
The AMR device is a device which uses a ferromagnetic body exhibiting the anisotropic magnetoresistance effect. The ferromagnetic body used in the AMR device preferably has a single domain so as to reduce the Barkhausen noise caused by movement of a domain wall. As an AMR device which reduces the Barkhausen noise, there has been suggested an AMR device in which an antiferromagnetic body is provided adjacent to a ferromagnetic body exhibiting the anisotropic magnetoresistance effect. In the AMR device of such configuration, the exchange interaction between the antiferromagnetic body and the ferromagnetic body controls a domain of the ferromagnetic body so as to establish a single domain, suppressing the Barkhausen noise caused by a domain wall.
On the other hand, the GMR device is a device which has a layered structure and changes its resistance value according to the giant magnetoresistance effect, and normally exhibits a larger resistance change than the AMR device. The GMR can be divided into two main types: a device having a comparatively complicated structure, i.e., superstructure and a device having a comparatively simple structure, i.e., spin bulb structure and changing its resistance value in a weak magnetic field.
The GMR device of the spin bulb structure at least has a first ferromagnetic layer, a non-magnetic layer, and a second ferromagnetic layer, which are successively stacked on each other. That is, in the GMR device of the spin bulb structure, the first ferromagnetic layer is separated from the second ferromagnetic layer by a thin non-magnetic layer, and an antiferromagnetic layer is provided on the first ferromagnetic layer.
In the GMR device, the first ferromagnetic layer adjacent to the antiferromagnetic layer has a fixed magnetization direction because of a magnetic connection with the antiferromagnetic layer, whereas the second ferromagnetic layer adjacent to the non-magnetic layer readily changes its magnetization direction according to an external magnetic field.
When the GMR device having such a configuration is subjected to an external magnetic field, the first ferromagnetic layer does not change its magnetization direction, and the second ferromagnetic layer alone changes its magnetization direction. The resistance value increases as an angle defined by the magnetization direction of the first ferromagnetic layer and the magnetization direction of the second ferromagnetic layer increases. This is because electrons which move between the first ferromagnetic layer and the second ferromagnetic layer are scattered in the boundary between the non-magnetic layer and first ferromagnetic layer and in the boundary between the non-magnetic layer and the second ferromagnetic layer.
As has been described above, in the AMR device and the GMR device, an antiferromagnetic body is used so as to control the magnetization state of the magnetic bodies in the device. Such an antiferromagnetic body conventionally used is an Fe-Mn alloy having a structure of a face-centered cubic (hereinafter, referred to as fcc structure). However, the Fe-Mn alloys have a problem that corrosion is easily caused by oxidation or the like.
Consequently, for example, when a magnetic head employing an MR device using an Fe-Mn alloy is produced, an antiferromagnetic layer made from the Fe-Mn alloy corrodes through oxidation or the like during an MR head production step, and it is impossible to obtain a preferable magnetic property.
To cope with this, there has been suggested to use a Ni-Mn alloy, Cr-Mn alloy, or NiO which is already an oxide, instead of the Fe-Mn alloy.
However, when such an antiferromagnetic body is provided adjacent to a ferromagnetic body so as to control the magnetization state, the antiferromagnetic layer should have a thickness required for obtaining an adequate magnetic property, which is about three times or more of the case when an antiferromagnetic body such as an Fe-Mn alloy is used. That is, it is necessary to increase the layer thickness when using a Ni-Mn alloy, Cr-Mn alloy, or NiO for controlling the magnetization state of the ferromagnetic body in the MR device.
Further, when an MR device having such an antiferromagnetic layer of increased thickness is employed in a magnetic head for reproduction, the magnetic gap for reproduction is also widened. That is, in a magnetic head using an MR device, a spacing between the magnetic shields provided at the both ends of the MR device is increased. This leads to that when reproducing a magnetic recording medium of a high recording density, a signal magnetic field other than those to be reproduced is also detected by this magnetic head. Thus, it is difficult to employ an MR device using an antiferromagnetic body requiring a large thickness, to a magnetic head for reproducing a magnetic recording medium having a high recording density.